Vehicle engine systems may include variable geometry turbochargers to supply compressed air and recirculated exhaust gas to the cylinders of the engine to increase operating efficiency, reduce emissions, and improve performance of the engine system. The variable geometry turbocharger may include vane(s) that may be adjusted via an actuator to alter the geometry of the turbine housing which in turn may affect exhaust flow of the variable geometry turbocharger. For example, at lower engine speeds with lower exhaust flow, the vanes may be adjusted to decrease the area of the variable geometry turbocharger intake in order to accelerate the exhaust gas causing the turbocharger turbine to spin faster thus reducing spool up time. As another example, at higher engine speeds with higher exhaust flow, the vanes may be adjusted to increase the area of the variable geometry turbocharger intake so as not to inhibit exhaust flow thus improving the efficiency of the variable geometry turbocharger. Accordingly, the vane(s) of the variable geometry turbocharger may be adjusted across the operating range of the engine system to increase efficiency of the variable geometry turbocharger.
A vane position sensor may be implemented to measure the position of the vane(s) in the variable geometry turbocharger so that accurate control of the variable geometry turbocharger may be achieved. However, degradation of the position sensor over time may decrease control accuracy of the variable geometry turbocharger, and may necessitate additional sensor diagnostics which can add considerable complexity to the overall system.
In one approach, a variable geometry turbocharger vane position may be estimated based on exhaust back pressure. In particular, a desired back pressure may be compared to a measured exhaust back pressure to determine the difference between a desired and measured exhaust back pressure. The difference may be used to determine the duty cycle for the variable geometry turbocharger. See, for example, U.S. Pat. No. 6,418,719.
However, the inventors herein have recognized some issues relating to the above approach. In particular, the above approach requires a sensor to measure exhaust back pressure, and such a sensor may not be present, or may be of insufficient accuracy to provide accurate position sensor estimation.
In one approach described herein, at least some of the above issues may be addressed by a method of operation for an engine system, the engine system having a variable geometry turbocharger with a vane, the vane having a variable position, the method comprising: adjusting a vane of the variable geometry turbocharger through a range of operation by stepping through a plurality of positions and holding at each of the plurality of positions, the range spanning from a substantially minimum position to a substantially maximum position of the variable geometry turbocharger; and adjusting operation of the engine based on a response to the vane adjustment.
In this way, aspects of engine operation may be controlled based on a vane position of a variable geometry turbocharger that may be accurately estimated without the need for a sensor to measure vane position (although a sensor additionally may be used, if desired to further improve accuracy). In other words, by intrusively stepping the vane through substantially the entire operating range from minimum to maximum (or maximum to minimum), the vane position may be repeatedly calibrated to a response parameter that may be used to accurately estimate vane position throughout vehicle operation.
Furthermore, an engine system that includes a vane position sensor may be made more robust by comparing the estimated vane position with a measured vane position in order to detect sensor performance degradation. In some embodiments, the inferred vane position may be used to infer an exhaust back pressure and exhaust system operation may be adjusted based on the inferred exhaust back pressure. Thus, by accurately inferring exhaust back pressure the need for an exhaust back pressure sensor may be eliminated and engine system robustness may be improved.